There was a common theme amongst many of the players who were released last week — guys like Steelers left tackle Levi Brown and linebacker Larry Foote, Vikings tight end John Carlson, Broncos cornerback Champ Bailey, Eagles receiver Jason Avant, Bears kick returner Devin Hester, Jaguars guard Uche Nwaneri, and Redskins defensive end Adam Carriker.

They’re all on the wrong end of 30 (in Nwaneri’s case, he’ll get there next week).

The NFL has never been an old man’s game, but with free agency set to begin on Tuesday, the league appears to be trending even younger, and it’s becoming tougher and tougher for 30-year-olds to find a roster spot, outside of quarterbacks, offensive linemen, and specialists.

“Teams are like, let us get through the rookies and get through the young free agents, and then we’ll go from there,” said one agent who represents a handful of over-30 free agents.

Only recently has reliable data on player ages been tracked, but it shows a clear trend toward younger players.

ESPN’s Mike Sando has recorded the ages of every player on opening day since the start of the 2010 season, and came up with the following average ages:

2010: 26.92 years

2011: 26.85 years

2012: 26.70 years

2013: 26.61 years

The .31 difference between 2010 and 2013 doesn’t seem large, but consider it’s for 53 players on 32 teams, equating to 525.76 fewer years of experience on the field between the two seasons.

In 2008, the Dallas Morning News wrote that the Redskins had the oldest lineup in the NFL at 28.63 years, the first time in that decade that the league’s oldest lineup did not average at least 29 years.

And age stats kept by pro-football-reference.com helped us determine that the number of players age 30 and over is trending downward since the start of 2010:

2010: 380 players age 30 and over

2011: 378 players

2012: 326 players

2013: 312 players

Several agents point to the new collective bargaining agreement, signed before the 2011 season, for the trend toward younger players. One of the biggest differences in the new CBA is that draft picks are now locked into low-paying contracts for three or four seasons — by rule, rookies cannot even renegotiate their contracts until after Year 3. While a few elite players earn huge paydays in free agency, most teams are now choosing young, cheaper players instead of more expensive veteran free agents.

And if over-30 veterans do stick to a roster, they are often asked to either take a pay cut or restructure their contracts to more team-friendly terms. The Steelers did that with Troy Polamalu last week, and the Patriots may do that soon with Vince Wilfork.

“That’s the flaw in the CBA,” the agent said. “It’s all about first-to-third-year players and paying as little money as possible on average and below-average guys. Now the big guys are getting huge money, and the middle class has basically evaporated.”

Young free agents — those in their mid-20s — can still cash in during free agency. The salary cap unexpectedly rose to $133 million, so teams have a little extra money to spend. Top players like Jairus Byrd, T.J. Ward, Eric Decker, and Aqib Talib should sign for big money this week. And talented veterans like Carlson and linebacker D’Qwell Jackson were able to sign with new teams last week — Carlson with Arizona and Jackson with Indianapolis — while Hester should find work quickly, as well.

But the days of having older veterans serve as backups and locker room leaders may be coming to an end. A few locker rooms with young quarterbacks will likely have the need for respected veteran backups, but the salary structure is pricing many of them out of the league.

In 2014, the minimum salary for players with 7-9 years of experience is $855,000, and $955,000 for 10-plus years. Compare that with rookies ($420,000) and second-year players ($490,000) and it’s easy to see why the league is trending younger.

“In 20-even years as an agent I never heard teams talk more about players’ ages than they do now,” agent Jack Bechta wrote in an interesting piece for National Football Post. “If you are on the wrong side of 30, not named Manning, Brady, or Brees, you may as well be ready for a tap on the shoulder any day to be shown the exit.”

One AFC director of pro personnel said that it’s good to have a few veterans on the roster to have balance in the locker room, and that each veteran must be dealt with on a case-by-case basis. But on the whole, the young players are better investments.

“You have to be cautious with aging veterans,” he said. “Even if there are no signs of hitting the wall, you know it’s coming, and you don’t want to be committed to guarantees that will hurt you if you discover it too late.”

COST EFFICIENCY

Patriots can learn from fiscal maneuvers

A few deals were struck last week that could affect some current Patriots players and their free agents.

Miami cornerback Brent Grimes got $16 million guaranteed over the next two seasons — a $6 million signing bonus and $10 million in salary — and that should serve as the floor for Aqib Talib, who is 2½ years younger and 2 inches taller than Grimes.

Buffalo gave a contract extension to safety Aaron Williams that should help serve as a guide for Devin McCourty as he enters the final year of his contract. A league source said the Patriots hadn’t contacted McCourty’s representatives about an extension as of Friday, but it would make sense to lock him up this offseason and lower his 2014 cap number from $5.115 million.

Williams, a three-year veteran who will turn 24 in April, signed a four-year extension through 2018 for $26 million overall and $14.625 million guaranteed. Williams, like McCourty, is a converted cornerback. He had a breakout year with four interceptions and 14 starts last season.

The Packers have reportedly offered nose tackle B.J. Raji a one-year deal worth $4 million, meaning Vince Wilfork should be able get $6 million or $7 million if the Patriots can convince him to take a new contract that will lower his cap number from $11.6 million.

And we hope that both Wilfork and the Patriots were paying attention to the new contract agreement between Troy Polamalu and the Steelers. Polamalu, like Wilfork, is an aging star whose 2014 cap number was too high, but the sides came to a reasonable agreement that lowered Polamalu’s number and prevented the team from having to cut a fan favorite.

Instead of an $8.25 million salary, the Steelers turned $7 million into bonus money and signed Polamalu through the 2016 season at base salaries of $1.25 million, $6 million, and $5.75 million. The Patriots and Wilfork should use a similar structure to avoid something drastic like having to cut him.

ON AN OUT ROUTE?

Three years in, Mallett still has plenty to prove

Patriots backup quarterback Ryan Mallett hasn’t gotten many opportunities to display his skills since the Patriots made him a third-round pick in 2011. Sitting patiently behind Tom Brady, Mallett has thrown four career passes — with one completion and one interception — and has completed less than 54 percent of his 206 preseason pass attempts, with seven touchdowns and three interceptions.

That’s why Mallett needs to take advantage of every opportunity if he’s ever going to be a starting quarterback in the NFL. Mallett, entering the final year of his contract, returned to his alma mater of Arkansas last week to serve as the throwing quarterback during the Razorbacks’ Pro Day.

Every NFL team had at least one coach or scout in attendance, and it served as a good opportunity for Mallett to show whether he had improved much since the pre-draft process in 2011.

But according to at least one report, Mallett’s performance was similar to his performance in three preseasons with the Patriots — a bit underwhelming. CBS Sports draft expert Rob Rang quoted a scout as saying that Mallett, listed at 6 feet 6 inches and 245 pounds, still looks gangly and “weak physically.” The scout described Mallett’s performance as “OK,” although he noted that his most impressive throws were deep outs and go routes, which are two of the most important throws in the NFL.

The Patriots have an interesting dilemma with Mallett. It’s highly unlikely they will score a first- or second-round pick for him, and even recouping a third-round pick seems unreasonable. That leaves them with three options. Given that he’s entering a contract year, they can try to trade him for a low-round pick and draft or sign another backup this year. They can let him play out his final year and try to re-sign him next season. Or they could simply let him play out his contract and walk away in free agency, and worry about finding Brady’s next backup next year.

ETC.

Dumping Amendola can cut both ways

There has been at least one report that the Patriots are shopping receiver Danny Amendola and considering releasing him after a disappointing 2013 season. They would then theoretically use his salary cap savings to retain free agent Julian Edelman, with whom the Patriots have begun initial talks on a contract extension, per ESPN.

The only logical way to cut Amendola would be via the June 1 cut, in which the Patriots would take on $1.2 million in dead cap space in 2014 and $3.6 million in 2015 (otherwise, it would be more expensive to outright cut Amendola than to keep him on the roster). A decision will come by Tuesday, when $2 million of Amendola’s $3 million base salary becomes guaranteed if he’s still on the roster.

The NFL Network reported last week that the Patriots cannot use the June 1 cut on Amendola because he automatically receives his bonus on Tuesday, the first day of the league year (and the first day Amendola could be cut), but that’s not quite accurate, the way we understand it. The league year begins at 4 p.m., and the Patriots will have until 11:59 p.m. Tuesday to decide whether or not to keep Amendola. If Amendola is still on the roster at midnight, then he gets his $2 million, and the Patriots lose incentive to cut him.

It’s highly unlikely the Patriots would ever sign a contract that would take away their ability to cut an underperforming player. That said, Amendola’s $4.575 million cap number isn’t exorbitant, and the Patriots shouldn’t have a burning need to cut him.

Parcells checks in

He hasn’t officially worked for an NFL team since the start of the 2010 season and he was inducted into the Hall of Fame last August, but Bill Parcells
can’t stay away from the game, apparently.

NFL Network’s Gil Brandt, the Cowboys’ top personnel man under Tom Landry for close to three decades, revealed last week that Parcells met with Browns owner Jimmy Haslam in Florida, where Parcells spends his winters, to serve as a courtesy consultant for the team. The Browns, of course, have had quite a tumultuous offseason in firing their head coach, GM, and team president, but have good pieces on the roster and hold the No. 4 and No. 26 picks in May’s draft.

Parcells also told Brandt that he met with Louisville quarterback Teddy Bridgewater, a possibility for the Browns with the fourth pick, for more than four hours in Florida, and that he was impressed with Bridgewater’s humility and football knowledge.

Lawsuit is latest fallout

The Richie Incognito-Jonathan Martin story just won’t go away. The latest development came last week when former head trainer Kevin O’Neill, unceremoniously fired after 18 years with the team, hired a lawyer and intends to sue the Dolphins for wrongful termination. The Dolphins contend that O’Neill did not do enough to stop the bullying, and was not cooperative with Ted Wells’s investigation into the matter.

“The Wells Report comes nowhere near supporting the decision of the Dolphins’ management to sack Mr. O’Neill,” his attorneys wrote in a lengthy rebuttal, via the Palm Beach Post. “Instead it demonstrates that Kevin O’Neill was improperly singled out to placate an understandable public outcry for action in response to what was publicly portrayed as intolerable workplace bullying.”

Location, location, location

An interesting study was released by Emory University last week that used Twitter reactions to gauge which cities would be the most and least receptive to having Michael Sam, the openly gay draft prospect, on their team.

Tweets were sorted by city and analyzed for positive, negative, or neutral sentiment.

The top five most receptive cities were New York, St. Louis (Sam went to Missouri), Chicago, San Francisco, and Boston, while the five least were Nashville, Oakland, Green Bay, Pittsburgh, and San Diego.

Quick slants

Interesting to see the Bills pull out of their Toronto series for 2014, announcing last week that the team will instead play all eight home games in Buffalo. The Bills had played one game a year in Toronto since 2008, with sluggish ticket sales. The team is supposed to play in Toronto through 2017, but it’s possible that the team and Rogers Centre may agree to scrap the deal altogether . . . One of the shames of the NFL system is how players are quickly discarded and forgotten. Receiver Davone Bess
was released by the Browns last week after one unproductive season and a string of bizarre behavior in recent weeks that led to him getting arrested in the Fort Lauderdale Airport for assaulting a police officer. Bess is clearly going through some mental issues, but now that he’s a free agent, he loses the support system that a team provides and doesn’t have as many people looking out for his well-being. We wish Bess luck in working through his issues.

Ben Volin can be reached at Ben.Volin@globe.com. Follow him on Twitter @BenVolin. Material from interviews, wire services, other beat writers, and league and team sources was used in this report.